This invention is generally directed to imaging members, and, more specifically, the present invention is directed to multilayered imaging members with two photogenerating layers, one of which is sensitive to a wavelength of from about 500 to about 800 nanometers, such as BZP, reference U.S. Pat. No. 4,587,189, the disclosure of which is totally incorporated herein by reference, and one of which is sensitive to a wavelength of from about 550 to about 950 nanometers, reference for example U.S. Ser. No. 332,304, the disclosure of which is totally incorporated herein by reference, especially Type V hydroxygallium phthalocyanine. The photogenerating layers can be exposed to light of the appropriate wavelengths simultaneously, sequentially, or alternatively only one of the photogenerating layers can be exposed. The imaging members of the present invention in embodiments exhibit excellent cyclic stability, independent layer discharge, and substantially no adverse changes in performance over extended time periods. Processes of imaging, especially xerographic imaging and printing, are also encompassed by the present invention. The aforementioned photoresponsive, or photoconductive imaging members can be negatively charged when the photogenerating layers are situated between the hole transport layers and the substrate, or positively charged when the hole transport layers are situated between the photogenerating layers and the supporting substrates. The layered photoconductive imaging members can be selected for a number of different known imaging and printing processes including, for example, electrophotographic imaging processes, especially xerographic imaging and printing processes wherein negatively charged or positively charged images are rendered visible using toner compositions of appropriate charge polarity. The imaging members as indicated herein are in embodiments sensitive in the wavelength region of from about 550 to about 900 nanometers, and in particular, from 700 to about 850 nanometers, thus diode lasers can be selected as the light source. Moreover, the imaging members of this invention are preferably useful in color xerographic applications where several color printings can be achieved in a single pass.
Photoresponsive imaging members with BZP alone, and hydroxygallium alone as a photogenerator pigment are known. These conventional photoresponsive imaging members are usually comprised of a single generator and a single transport layer, and they are used in xerographic printing processes to perform one pass/one color printing. Multiple color printing requires repeating the process several times depending on the number of colors selected. More recently, trilevel xerographic processes are known where two color printing can be achieved in a single pass. In the trilevel xerographic process, the conventional photoresponsive imaging members are used in one pass/two color printing processes. The imaging member is selectively discharged with a single laser source to create three potential levels and later toned to create two color printing.
Thus, there remains a need for improving the color printing capability of xerographic processes, and in particular, to print more colors with a minimum number of passes, and therefore, improve the productivity of the printing process. This can be achieved with the imaging members of the present invention wherein there are sequentially arranged four layers. These imaging members can be referred to as multilayered two-tier photoresponsive imaging member. The photodischarge behavior of two-tier imaging members is selectively controlled by the wavelengths of exposure light and hence the member can be fully discharged, partially discharged or zero discharged. There can be two possible partially discharged areas depending on the location of the photodischarge, top tier discharged or bottom tier discharge. The fully discharged and zero discharged areas can be developed with appropriate toners to provide two different colors. Also, a flood expose with a light effective on only the top tier can be employed to remove its partial charge to zero. The zero charge area can then be developed with another color toner. With two lasers of selected wavelengths, one effective on the top tier, the other on the bottom tier, and applying a further flood discharge on the top tier, three color printing in a single pass is achieved.
There is illustrated in JPLO 221459 a photoreceptor for use in electrophotography comprising a charge generation material and charge transport material on a conductive substrate, and wherein the charge generation material comprises phthalocyanine compounds which show the following intense diffraction peaks at Bragg angles (2 theta +/-0.2.degree.) in the X-ray diffraction spectrum,
1--6.7, 15.2, 20.5, 27.0;
2--6.7, 13.7, 16.3, 20.9, 26.3; and
3--7.5, 9.5, 11.0, 13.5, 19.1,20.3, 21.8, 25.8, 27.1, 33.0.
In Konica Japanese 64-17066/89, there is disclosed, for example, the use of a new crystal modification of titanyl phthalocyanine (TiOPc) prepared from alpha-type TiOPc (Type II) by milling it in a sand mill with salt and polyethylene glycol. This publication also discloses that this new polymorph differs from alpha-type pigment in its light absorption and shows a maximum absorbance at 817 nanometers while the alpha-type exhibits a maximum at 830 nanometers. The Konica publication also discloses the use of this new form of TiOPc in a layered electrophotographic device having high photosensitivity at exposure radiation of 780 nanometers. Further, this new polymorph of TiOPc is also described in U.S. Pat. No. 4,898,799 and in a paper presented at the Annual Conference of Japan Hardcopy in July 1989. In this paper, this same new polymorph is referred to as Type Y, and reference is also made to Types I, II, and III as A, B, and C, respectively.
Layered photoresponsive imaging members have been described in a number of U.S. patents, such as U.S. Pat. No. 4,265,900, the disclosure of which is totally incorporated herein by reference, wherein there is illustrated an imaging member comprised of a photogenerating layer, and an aryl amine hole transport layer. Examples of photogenerating layer components include trigonal selenium, metal phthalocyanines, vanadyl phthalocyanines, and metal free phthalocyanines. Additionally, there is described in U.S. Pat. No. 3,121,006 a composite xerographic photoconductive member comprised of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The binder materials disclosed in the '006 patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles.
The use of certain perylene pigments as photoconductive substances is also known. There is thus described in Hoechst European Patent Publication 0040402, DE3019326, filed May 21, 1980, the use of N,N'-disubstituted perylene-3,4,9,10-tetracarboxyldiimide pigments as photoconductive substances. Specifically, there is, for example, disclosed in this publication N,N'-bis(3-methoxypropyl)perylene-3,4,9,10-tetracarboxyldiimide dual layered negatively charged photoreceptors with improved spectral response in the wavelength region of 400 to 700 nanometers. A similar disclosure is revealed in Ernst Gunther Schlosser, Journal of Applied Photographic Engineering, Vol. 4, No. 3, page 118 (1978). There are also disclosed in U.S. Pat. No. 3,871,882 photoconductive substances comprised of specific perylene-3,4,9,10-tetracarboxylic acid derivative dyestuffs. In accordance with the teachings of this patent, the photoconductive layer is preferably formed by vapor depositing the dyestuff in a vacuum. Also, there are specifically disclosed in this patent dual layer photoreceptors with perylene-3,4,9,10-tetracarboxylic acid diimide derivatives, which have spectral response in the wavelength region of from 400 to 600 nanometers. Also, in U.S. Pat. No. 4,555,463, the disclosure of which is totally incorporated herein by reference, there is illustrated a layered imaging member with a chloroindium phthalocyanine photogenerating layer. In U.S. Pat. No. 4,587,189, the disclosure of which is totally incorporated herein by reference, there is illustrated a layered imaging member with, for example, a BZP perylene, pigment photogenerating component. Both of the aforementioned patents disclose an aryl amine component as a hole transport layer.
Illustrated in U.S. Pat. No. 5,382,492 the disclosure of which is totally incorporated herein by reference, are processes for the preparation of Type II dihydroxygermanium phthalocyanine, which comprises the reaction of phthalonitrile or diiminoisoindolene with tetrahalogermanium or tetraalkoxygermanium in a suitable solvent, treatment of the resultant dihalogermanium phthalocyanine or dialkoxygermanium phthalocyanine intermediate with concentrated sulfuric acid, and then water, and filtering and washing of the dihydroxygermanium phthalocyanine precipitate with water using care that the filtrate of the washing does not exceed a pH of 1.0, removing the absorbed acid on the dihydroxygermanium phthalocyanine product with an organic base, such as amine, and optionally washing the pigment crystals with an aprotic organic solvent, such as an alkylene halide like methylene chloride, tetrahydrofuran, or dimethylformamide; and the preparation of Type II dihydroxygermanium phthalocyanine by polymorphic conversion from other polymorphs, such as Type I polymorph, by simply treating with concentrated sulfuric acid, followed by the same washing processes as described above. The different polymorphic forms of dihydroxygermanium phthalocyanine can be readily identified by various known analytical methods including solid state absorption spectra and X-ray powder diffraction analysis (XRPD).
Also, in U.S. Pat. No. 5,473,064, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of hydroxygallium phthalocyanine Type V, essentially free of chlorine, whereby a pigment precursor Type I chlorogallium phthalocyanine is prepared by reaction of gallium chloride in a solvent, such as N-methylpyrrolidone, present in an amount of from about 10 parts to about 100 parts, and preferably about 19 parts with 1,3-diiminoisoindolene (DI.sup.3) in an amount of from about 1 part to about 10 parts, and preferably about 4 parts DI.sup.3, for each part of gallium chloride that is reacted; hydrolyzing said pigment precursor chlorogallium phthalocyanine Type I by standard methods, for example acid pasting, whereby the pigment precursor is dissolved in concentrated sulfuric acid and then reprecipitated in a solvent, such as water, or a dilute ammonia solution, for example from about 10 to about 15 percent; and subsequently treating the resulting hydrolyzed pigment hydroxygallium phthalocyanine Type I with a solvent, such as N,N-dimethylformamide, present in an amount of from about 1 volume part to about 50 volume parts and preferably about 15 volume parts for each weight part of pigment hydroxygallium phthalocyanine that is used by, for example, ball milling said Type I hydroxygallium phthalocyanine pigment in the presence of spherical glass beads, approximately 1 millimeter to 5 millimeters in diameter, at room temperature, about 25.degree. C., for a period of from about 12 hours to about 1 week, and preferably about 24 hours such that there is obtained a hydroxygallium phthalocyanine Type V; ball milling contains very low levels of residual chlorine of from about 0.001 percent to about 0.1 percent; and in an embodiment about 0.03 percent of the weight of the Type V hydroxygallium pigment, as determined by elemental analysis.
The disclosures of all of the aforementioned publications, laid open applications, copending applications and patents are totally incorporated herein by reference.